Every 100 kcal of onion brings 2.8 g of protein. On that measure it ranks 77th of the 105 vegetables in this database and 639th of all 796 foods on the site. Measured by weight instead, its 1.1 g per 100 g ranks 76th in its group.
Only about 11% of the calories in onion come from protein, so it is more of an energy food than a protein food. It is worth eating for other reasons; the protein it adds to a day is incidental.
USDA lists 0.1 g of fat per 100 g of onion, too little for a protein-to-fat ratio to mean much.
Set against alfalfa sprouts, another vegetable entry in the database, a serving carries about 0.5 g more protein (alfalfa sprouts has 1.3 g per 1 cup).
It is an incomplete protein on its own; pairing it with other plant foods across the day covers the full range of essential amino acids. The serving quoted here is measured by volume at 160 g, and it covers about 4% of the 50 g FDA Daily Value for protein.
Serving sizes
Protein in common portions of onion
Protein and calories in Onion for 100 g, the site serving and USDA household portions.
Portion
Weight
Protein
Calories
100 g
100 g
1.1 g
40 kcal
1 cup chopped (serving used here)
160 g
1.8 g
64 kcal
1 cup, sliced
115 g
1.3 g
46 kcal
1 tbsp chopped
10 g
0.1 g
4 kcal
1 large
150 g
1.7 g
60 kcal
1 slice, large (1/4" thick)
38 g
0.4 g
15 kcal
1 medium (2-1/2" dia)
110 g
1.2 g
44 kcal
Portion weights are the household measures listed on the USDA record; protein and calories scale from the per-100 g figures.
Amino acids
Essential amino acids in onion
The nine essential amino acids in Onion, per 100 g, per serving and per gram of protein.
Amino acid
Per 100 g
Per serving
mg per g protein
leucine
0.025 g
0.04 g
23
lysine
0.039 g
0.06 g
35
valine
0.021 g
0.03 g
19
isoleucine
0.014 g
0.02 g
13
threonine
0.021 g
0.03 g
19
phenylalanine
0.025 g
0.04 g
23
methionine
0.002 g
0 g
2
histidine
0.014 g
0.02 g
13
tryptophan
0.014 g
0.02 g
13
Per-100 g values are the amino acid analysis on the USDA record. The serving and per-gram-of-protein columns are arithmetic on those values; they are not a protein quality score.
SampleWhat goal trends look like after a week
109 g
Average per logged day
4 of 7
Days goal met
71%
Complete-protein share
Mon
Tue
Wed
Thu
Fri
Sat
Sun
Sample figures for one made-up week against a 110 g goal, not your data. Red bars met the goal. Your own log fills this in with Premium.
1.1 g. The 1 cup chopped serving used on this page weighs 160 g and so carries 1.8 g.
How much protein do you get per 100 calories of onion?
2.8 g. That figure divides its 1.1 g of protein per 100 g by its 40 kcal per 100 g, so it does not depend on serving size.
Is the protein in onion complete?
No. On its own, the protein in onion is short of at least one essential amino acid; other protein sources across the day fill the gap.
What share of the protein Daily Value is one serving of onion?
About 4%. One 1 cup chopped serving has 1.8 g, and the FDA Daily Value for protein is 50 g.
Figures from USDA FoodData Central record #170000 (Onions, raw), SR Legacy data. USDA data is in the public domain. Values are the published reference figures for that record, not lab measurements for a specific brand or batch.